An eight-month construction standstill at a North Korean site meant to launch bigger and better long-range rockets may signal Pyongyang is slowing or even stopping development of larger rockets, according to a new analysis of recent satellite imagery.

Roads lie unfinished and grass is growing from the foundation of a large new rocket assembly building, according to analysis by 38 North, the website for the US-Korea Institute at Johns Hopkins school of advanced international studies.

It is unknown if the work stoppage on the launch pad, rocket assembly building and launch control centre at the Tonghae satellite launching ground is only temporary.

But the analysis of 26 May commercial satellite imagery provides some theories.

One is that equipment and construction troops sent from the site to help repair widespread rain damage last year may still be at other posts. Another is that North Korea's leadership has decided that its more modern Sohae rocket launching site on the north-west coast, used to launch rockets in April and December 2012, will be sufficient to support large rocket development

But the most intriguing theory from the analysis is that the work stoppage could reflect a decision in Pyongyang to slow or stop building larger rockets.

"If Pyongyang ultimately abandons facilities to launch large rockets it only began building in 2011, that could have important implications for North Korea's space launch programme as well as the development of long-range missiles intended to deliver nuclear weapons," Joel Wit, a former US State Department official and now editor of 38 North, said in an email.

Washington sees North Korea's secretive rocket programme as a cover for work on missiles that could strike the US mainland.

The analysis said there was no sign of activity, equipment or personnel at the new launch pad at Tonghae. Grass is growing from the foundation of a large new rocket assembly building, and work is incomplete on a road meant to bring construction equipment and, eventually, large rocket stages to the site.

Even if North Korea resumed work at the site, the delay means completion could be pushed back to 2017, at least a year longer than earlier estimates, according to the analysis.

Earlier this year, North Korean leader Kim Jong-un enshrined the drive to build a nuclear arsenal, as well as expand the economy, in North Korea's constitution.

Since 2006, North Korea has staged three nuclear tests of apparently increasing power and a series of long-range rocket launches. North Korea says its rocket launches are meant to put peaceful satellites into orbit.

North Korea reacted with fury to UN sanctions that followed a nuclear test this year and the December rocket launch, threatening nuclear war on Washington and Seoul.